1. Field of the Invention
This invention relates to the field of electric pianos incorporating electromagnetic mechanical-electrical transducers (commonly referred to as electromagnetic pickups).
2. Description of the Prior Art
Because of their portability, their ability to remain in tune over long periods of time, their ability to be heard either by large numbers of people or (with earphones) only by the pianist himself, and their ability to generate numerous vibrato and tonal effects, electric pianos are becoming increasingly popular. Of electric pianos, the best are the electromechanical type in which the strings of conventional pianos are replaced by vibrating tines or reeds. The vibrations of the tines or reeds are sensed by pickups, thus generating voltage signals which are electronically amplified and fed to a loudspeaker.
A major problem relating to such electromechanical pianos resulted from the fact that vibrating tines or reeds normally have dissonant overtones which are not at all pleasing to the ear. These overtones are not harmonics (integral multiples of the fundamental frequency). In this respect, tines or reeds are to be contrasted with conventional piano strings, wherein the overtones are substantial harmonics and are pleasing to the ear.
The problem stated in the preceding paragraph, and other important problems, were solved as set forth in U.S. Pat. No. 2,972,922, inventor H. B. Rhodes. The invention stated in such patent, together with later Rhodes inventions as described (for example) in U.S. Pat. Nos. 3,384,699, 3,418,417, 3,644,656, produced a highly successful piano which is popular with large numbers of professional and other musicians.
There has, however, long existed a desire for an electromechanical tine-type piano which sounds more in the nature of a conventional string-type acoustic piano, particularly in the mid-range of the piano. To accomplish this, it is necessary not only to eliminate the dissonant reed overtones (as was done by Rhodes) but also to cause introduction at the pickup of harmonics having a different and more acoustic piano-like "mix" or character than in the prior art. The present invention does this economically, simply and practically, and also achieves excellent apparent loudness and brightness of tone, with consequent minimized requirements for amplification. The present invention also permits generation of tones and chords, even in octaves below middle C, which are relatively acoustic piano-like in character.
With relation to certain prior art other than the stated Rhodes inventions, U.S. Pat. No. 3,038,363, inventor B. F. Miessner, discusses theories relating to the creation of piano-like tones by means of an electromechanical reed-type piano. Harmonic content, and the generation of asymmetrical peaked voltage waves, are discussed at length. However, the electromagnetic pickup structures taught by U.S. Pat. No. 3,038,363 (FIGS. 49 through 54), and by other Miessner U.S. patents such as No. 3,215,765, are expensive, inefficient, large, and (it is believed) incapable of accomplishing important results achieved by the present pickup. Another prior-art U.S. Pat. No. 2,581,963, inventor R. J. Langloys, shows in FIG. 22 an electromagnetic pickup of the general type used by Rhodes, and discusses a frequency-doubling effect which will be referred to later in this specification. Langloys also mentions that the shape of the pole piece extremity permits to grade the closing of the harmonics, but gives no indication of what shape to use or how or why to create any such "grading". A further U.S. Pat. No. 2,510,094, inventor E. O. Fleury, discloses an electromechanical piano of the type wherein the lines of magnetic force extend for the full length of the reed, and follow a substantially closed low-reluctance magnetic circuit, instead of looping back through the air around the coil. Fleury's object is to achieve sinusoidal variations of the magnetic flux, which variations (it is believed) produce dull tones very unlike those of an acoustic piano.
In summary, the prior art does not teach or suggest how to create, in a tine-type piano, acoustic piano-like sounds in a practical, economical, commercially feasible way -- with excellent brightness and apparent loudness and with the ability to generate acoustic piano-like tones and chords both below and above middle C.